1. Field of the Invention
The present invention relates to a surface acoustic wave (hereinafter, SAW) device and a method for manufacturing the same, and is particularly suitable for a SAW device where a plurality of SAW filters are accommodated in one package.
2. Description of the Related Art
In recent years, wide band filters are demanded in a mobile communication device of a multi-band correspondence type having two or more communication systems. However, it is difficult to realize a broadband filter with low loss, while covering two or more bands. Therefore, a SAW device constituted to accommodate a plurality of SAW filters in one package having a lid member for shielding has been widely used.
For example, Japanese Patent Application Laid-open (JP-A) No. 2002-208832 discloses an SAW device where a plurality of SAW filters are accommodated in one package, mutual interference between SAW filters can be reduced, and an attenuation amount outside a passing band can be increased.
A conventional SAW device described in JP-A No. 2002-208832 will be explained with reference to FIGS. 10 and 11.
FIG. 10 is a diagram showing a schematic constitution of the conventional SAW device shown in JP-A No. 2002-208832. In the conventional SAW device, a first SAW filter 51 and a second SAW filter 52 are accommodated in one package 53. The first SAW filter 51 has an unbalanced input signal terminal 54, a ground terminal 55, and balanced output signal terminals 56, 57, while the second SAW filter 52 has an unbalanced input signal terminal 58, a ground terminal 59, and balanced output signal terminals 60, 61.
FIG. 11 is a diagram showing a schematic structure of the SAW device shown in FIG. 10. In an SAW chip 62, the first SAW filter 51 and the second SAW filter 52 shown in FIG. 10 are formed on a surface of a piezoelectric substrate. Such an SAW chip 62 is then accommodated inside the package 53 by a face down process such that a face of the SAW chip 62 on which electrodes are formed is directed downwardly. The package 53 has a base board 53a and an annular side wall 53b fixed on the base board 53a. An upper opening of the annular side wall 53b is then sealed by a lid member 53c for shielding. Furthermore, an electrode land 53d is formed on the base board 53a. The electrodes of the SAW chip 62 are joined to the electrode land 53d via bumps 63 so that the SAW chip 62 and the package 53 are mechanically connected to each other and the electrodes of the SAW chip 62 and the electrode land 53d of the package 53 are electrically connected to each other.
Recently, along with the downsizing of mobile communication devices, such as a portable or cellar phone, demands for downsizing and thinning quartz-related parts used in these mobile communication devices are increasing. As shown in FIG. 11, however, since such a conventional SAW device as described above has a structure where the SAW chip 62 is bonded within the package 53 in a flip-chip manner, it is difficult to achieve further downsizing. In case of structure where the SAW chip 62 is accommodated within package 53, this is because it is necessary to make the size of the SAW device larger than an actual size of the SAW chip 62 by a size corresponding to two times a thickness d1 of each side walls 53b formed on both sides of the package 53 and two times a gap d2 between the sidewall 53b and the SAW chip 62, it is also difficult to thin the thickness d1 of the side wall 53b in view of a strength, and the gap d2 cannot be reduced from the aspect of manufacture.
That is, although the conventional SAW device is excellent in attenuation characteristics outside a passing band, downsizing cannot be achieved.
The present invention has been achieved in view of the above circumstances and an object thereof is to provide a SAW device where downsizing can be achieved without deteriorating attenuation characteristics outside a passing band, and a method for manufacturing the same.